This invention relates to a pin feed mechanism for transporting continuous stationery. The invention has particular application to a mechanism for transporting continuous forms paper in high-speed line printers.
High-speed line printers usually function as peripheral devices of electronic data processing systems for printing out information generated by such systems. As information is generated at extremely high speeds, the printers must also be capable of operating at high-speed, and typical line printers used for this purpose are capable of printing about 120 lines per minute.
The stationery used for high-speed printers of this kind is continuous and is usually fed from a roll or from a stack of fan-folded stationery. Typically, continuous forms paper is provided with feed apertures or perforations at both longitudinal edges of the paper to enable feed pins or sprockets of a transport mechanism to engage the apertures and advance the paper past the printing station to perform a "line feed", a "page feed" or a continuous feed, as required by the system program.
The feeding mechanism for transporting the continuous forms paper may contain a pair of feeding devices each including a sprocketed endless tractor belt and a pressure shoe between which the paper passes during the feeding operation, the pins or sprockets of each belt being arranged to engage with a respective series of perforations along a longitudinal edge of the paper. Alternatively, the feeding mechanism may include a drum or cylindrical platen having a series of pins around its periphery at either end. The advantage of the tractor belt arrangement is that the distance between the two feeding devices may be adjusted to accept papers or different widths.
A problem encountered with pin feed mechanisms of the above described types is that the pins penetrating the perforations of the paper tend to cause deformation or even tearing of the paper at the points of contact with the pins at the high rate of paper advance usual with conventional line printers. This may be particularly troublesome with multi-copy forms sets where the perforations are not always properly aligned, and deformation of the bottom forms paper may cause bulging of the set and jamming of the feed mechanism leading to a disruption of the printing operation.